The invention relates to new polymers based on alkenoyloxybenzylidenemalonic esters and their use as UV-absorbers for stabilizing plastics.
A large number of UV-absorbers is known (compare, for example, DT-OS 1,544,605 (corresponds to British Pat. No. 1,037,169) or DT-PS 1,987,902) but they possess a series of disadvantages. Thus, for example, yellowing and browning of UV-stabilized products is to be observed on continuous heat exposure. A further disadvantage of many previously known UV-absorbers is their volatility, which leads to considerably difficulties (loss by evaporation, loss by migration and the like), especially at higher processing temperatures.
Transparent polycarbonate molding compositions stabilized against UV-light which contain low molecular UV-absorbers are also known. The stabilization of polycarbonates, however, and especially pigmented polycarbonates, has not been satisfactory. The previously known and used UV-absorbers fail in the stabilization of polycarbonates in the presence of pigments. Evidently, interactions between polycarbonate, pigment surface and UV-light play a decisive role in this.